The present invention relates to an audio reproducing system for realizing a sound field with a reality sensation by correcting an interaural correlation for the listener.
In the related art, the multi-channel stereo system is known. This multi-channel stereo system intends to realize the sound field space with a reality sensation by supplying multi-channel audio signals to a plurality of loudspeakers to sound them.
For example, the multi-channel stereo system called the “5.1-channel system” is cited as the typical example. As shown in FIG. 7A, multi-channel audio signals FL, Cn, FR, LS, RS, LFE of 6 channels are power-amplified by the audio amplifiers AMPFL, AMPCn, AMPFR, AMPLS, AMPRS, AMPLFE respectively, and then supplied to the loudspeakers SPL, SPC, SPR, SPLs, SPRs, SPSW of independent 6 channels.
Then, as shown in FIG. 7B, the front-left loudspeaker SPL, the center-channel loudspeaker SPC and the front-right loudspeaker SPR are arranged in front of the listener A, and the left surround loudspeaker SPLs and the right surround loudspeaker SPRs are arranged in the back of the listener A, and the heavy low sound reproducing loudspeaker SPSW called as the sub-woofer (referred to as the “sub-woofer” hereinafter) is arranged at the appropriate position.
Then, all the audio signals FL, Cn, FR, LS, RS of five channels except the sub-woofer channel audio signal LFE are set to cover the full range (about 20 Hz to about 20 kHz) of the audio frequency band. The sub-woofer channel audio signal LFE is set to cover the low frequency range of about 20 Hz to about 120 Hz.
In this manner, unlike the so-called “four-channel stereo system” in which only four loudspeakers SPL, SPR, SPLs, SPRs arranged in front left, front right, rear left, and rear right sites are sounded, the “5.1-channel system” intends to realize the sound field space with the reality sensation by sounding the center loudspeaker SPc and the sub-woofer SPSW in addition to the above loudspeakers.
Also, the system that tends to realize the reality sensation that is identical to the “5.1-channel system” by utilizing few loudspeakers (referred to as the “pseudo system” hereinafter) is proposed.
In this pseudo system, as shown in FIG. 8A, the center-channel audio signal Cn based on the “5.1-channel system” is attenuated by the attenuator ATT, then the synthesized signal SL that is produced by synthesizing its attenuated signal Cn′ to the left channel audio signal FL by virtue of the adder ADDFL is supplied to the front-left loudspeaker SPL via the audio amplifier AMPFL, and then the synthesized signal SR that is produced by synthesizing its attenuated signal Cn′ to the right-channel audio signal FR by virtue of the adder ADDFR is supplied to the front-right loudspeaker SPR via the audio amplifier AMPFR.
In addition, the audio signals LFE, LS, RS based on the “5.1-channel system” are supplied to the sub-woofer SPSW, the rear-left surround loudspeaker SPLs, and the rear-right surround loudspeaker SPRs respectively.
Then, as shown in FIG. 8B, such pseudo system can provide the sound field that is able to give the reality sensation to the listener A, who is positioned in the almost center of four loudspeakers (so-called main loudspeakers) SPL, SPR, SPLs, SPRs arranged in front left, front right, rear left, and rear right sites, not to provide the center- channel loudspeaker SPC.
However, according to the above pseudo system in the prior art explained with reference to FIGS. 8A and 8B, if the position of the listener is deviated from the center position indicated by the symbol B in FIG. 8B, the phase differences are generated when the sound waves generated from respective loudspeakers SPL, SPR, SPLs, SPRs come into both ears of the listener. Therefore, the listener is caused to feel the unnatural sound image, or the unclearness of the sound image normal and the dangling-about of the sound, etc. are generated. As a result, there is the problem that the reality sensation is considerably spoiled.
Also, in case the loudspeakers equipped in the above-mentioned compartment are sounded by the pseudo system, the center-channel audio signal Cn is reproduced via the front-left and front-right loudspeakers SPL, SPR and thus the phase differences are generated when the regenerated sound waves reach both ears of the listener (the driver, or the like). Therefore, the listener is caused to feel the unnatural sound image normal, or the unclearness of the sound image normal and the dangling-about of the sound, etc. are generated. As a result, there is the problem that the reality sensation is considerably disturbed.
FIG. 2A shows the result of the influence of the phase difference in the sound waves that reach both ears of the driver (listener), which is measured quantitatively by using the binaural correlation coefficient ρLR when the loudspeakers SPL, SPR, SPLs, SPRs, SPSW in the compartment are caused to sound based on the pseudo system.
According to this measured result, the binaural correlation coefficient ρLR has the negative value in the range of about 200 Hz to about 600 Hz around about 400 Hz. This phenomenon signifies that the phase difference in the sound waves between both ears of the driver comes close to the opposite phase. It may be considered that this phenomenon causes the driver to feel the unnatural sound image normal or causes the unclearness of the sound image normal and the dangling-about of the sound, etc.
In addition, the range of about 200 Hz to about 600 Hz is used mainly as the vocal sound, the talk in the movie, etc. Therefore, there is the problem that the unclearness of the sound image normal and the dangling-about of the sound, etc. are generated. For instance, although essentially the driver hears the vocal sound (the speech of human beings, etc.) emitted from the front-left and front-right loudspeakers SPL, SPR from the front side, such driver feels to hear the vocal sound from the back of the driver's head.
The invention is made in view of the problems in the prior art, and it is an object of the invention to provide an audio reproducing system for realizing the natural sound image normal, etc. by correcting the listener's interaural correlation of the audio signal.
In order to achieve the above object, there is provided an audio synthetic system including:
input section for inputting a first audio signal, a second audio signal and a third audio signal;
dividing section for dividing the third audio signal into two divided third signals, which have a phase difference mutually in one frequency range;
a first synthetic section for synthesizing one of the two divided third signals and the first audio signal into a first synthetic signal; and
a second synthetic section for synthesizing the other of the two divided third signals and the second audio signal into a second synthetic signal.
Also, the audio synthetic system according to aspect 1, wherein
the dividing section sets the phase difference of the one of the two divided third signals and the other of the two divided third signals to 180 degree at maximum in the one frequency range, which is from 200 Hz to 2 kHz, and adjusts the phase difference from 180 degree at maximum to 0 degree toward frequencies of 200 Hz and 2 kHz.
According to the audio reproducing system having such configuration, two center-channel audio signals that have a phase difference mutually are generated from the center-channel audio signal supplied from the sound source. Here, in order to fit to the vocal sound, etc., the phase difference is set −180 (deg) at maximum in the frequency range of 200 Hz to 2 kHz, and the phase difference is adjusted from −180 (deg) at maximum to 0 (deg) toward the frequencies of 200 Hz and 2 kHz. Then, the first synthesized audio signal, which is generating by synthesizing one center-channel audio signal being subjected to the phase adjustment and the front-left channel audio signal, is supplied to the front-left channel loudspeaker. Also, the second synthesized audio signal, which is generating by synthesizing the other center-channel audio signal being subjected to the phase adjustment and the front-right channel audio signal, is supplied to the front-right channel loudspeaker.
In this manner, the binaural correlation coefficient of the sound being output from both front channel loudspeakers is corrected by supplying the center channel audio signal having the phase difference to the front-left channel loudspeaker and the front-right channel loudspeaker, and the natural sound image normal, etc. can be realized, and thus the sound field with the reality sensation can be provided.
Also, in order to achieve the above object, there is provided an audio synthetic system including:
input section for inputting a first audio signal, a second audio signal and a third audio signal;
separating section for separating the third audio signal into a high frequency signal and a low frequency signal at a predetermined frequency as a boarder, and outputting the high frequency signal;
dividing section for dividing the low frequency signal into two divided low frequency signals, which have a phase difference mutually in one frequency range;
a first synthetic section for synthesizing one of the two divided low frequency signals and the first audio signal into a first synthetic signal; and
a second synthetic section for synthesizing the other of the two divided low frequency signals and the second audio signal into a second synthetic signal.
Also, the audio synthetic system according to aspect 3, wherein
the dividing section sets the phase difference of the one of the two divided low frequency signals and the other of the two divided low frequency signals to 180 degree at maximum in the one frequency range, which is from 200 Hz to 2 kHz, and adjusts the phase difference from 180 degree at maximum to 0 degree toward frequencies of 200 Hz and 2 kHz.
Also, the audio synthetic system according to aspect 4, wherein
the separating section sets the predetermined frequency, from which the high frequency signal and the low frequency signal are separated, within a frequency range from a frequency, at which a phase is adjusted into 180 degree at maximum by the dividing section, to 2 kHz.
According to the audio reproducing system having such configuration, the predetermined high frequency component of the center channel audio signal is supplied to the center channel loudspeaker, the phase of the predetermined low frequency component of the center channel audio signal is adjusted, and the component is supplied to the front-left channel loudspeaker and the front-right channel loudspeaker. That is, two low frequency components that have a phase difference mutually in the predetermined frequency range are generated from the low frequency component. Then, the first synthesized audio signal, which is generating by synthesizing one low frequency component being subjected to the phase adjustment and the front-left channel audio signal, is supplied to the front-left channel loudspeaker. Also, the second synthesized audio signal, which is generating by synthesizing the other low frequency component being subjected to the phase adjustment and the front-right channel audio signal, is supplied to the front-right channel loudspeaker.
Here, in order to fit to the vocal sound, etc., the phase difference of two low frequency components is set −180 (deg) at maximum in the frequency range of 200 Hz to 2 kHz, and the phase difference is adjusted from −180 (deg) at maximum to 0 (deg) toward the frequencies of 200 Hz and 2 kHz. Also, the high frequency component and the low frequency component are separated within a frequency range from a frequency, at which the phase difference is adjusted into −180 (deg) at maximum, to 2 kHz.
Also, in order to achieve the above object, there is provided an audio synthetic method including:
inputting a first audio signal, a second audio signal and a third audio signal;
dividing the third audio signal into two divided third signals, which have a phase difference mutually in one frequency range;
synthesizing one of the two divided third signals and the first audio signal into a first synthetic signal;
synthesizing the other of the two divided third signals and the second audio signal into a second synthetic signal; and
outputting the first synthetic signal and the second synthetic signal.
Also, in order to achieve the above object, there is provided an audio synthetic method including:
inputting a first audio signal, a second audio signal and a third audio signal;
separating the third audio signal into a high frequency signal and a low frequency signal at a predetermined frequency as a boarder;
dividing the low frequency signal into two divided low frequency signals, which have a phase difference mutually in one frequency range;
synthesizing one of the two divided low frequency signals and the first audio signal into a first synthetic signal;
synthesizing the other of the two divided low frequency signals and the second audio signal into a second synthetic signal; and
outputting the first synthetic signal, the second synthetic signal and the high frequency signal.
In this manner, the binaural correlation coefficient of the sound being output from both front channel loudspeakers is corrected by supplying the low frequency component having the phase difference to the front-left channel loudspeaker and the front-right channel loudspeaker and also supplying the high frequency component of the center channel audio signal to the center channel loudspeaker, and the sound image of the vocal sound being output from the center channel loudspeaker can be positioned at the natural position, and thus the sound field with the reality sensation can be provided.